Paper distributing an active compound on burning, and a pyrotechnic distributor using such paper

ABSTRACT

Paper distributing an active compound such as a pesticide or a lachrymatory agent, particularly intended to be used in buildings or closed enclosures. 
     This paper is intended to be burnt to ensure the dissemination of the active compound incorporated in the paper. To ensure an efficient and rapid dissemination by means of a large volume of combustion gas containing only a little smoke and originating from a special combustion reaction at a limited temperature so as not to decompose the active compound, this paper is a nitrocellulose-based paper in which the proportion of nitrogen is greater than 5% and in which the fibres consist of a mixture of cellulose and nitrocellulose fibres, this mixture comprising at least 18% of cellulose fibres and the active compound having a decomposition temperature above 130° C.

The invention relates to distributing components consisting of acombustible substrate and at least one active compound such as apesticide or a lachrymatory agent, and more particularly papersdistributing active compounds of these types, which are particularlyintended to be burnt in buildings, for example in premises to bedisinfected or from which insects or rats are to be eliminated, or inenclosures which are at least partly closed, such as cultivation houses.

The invention also relates to fumigation devices, and more particularlyto pyrotechnic distributors which make use of active compoundsincorporated in a combustible substrate.

The distribution of active compounds by burning a substrate has beenknown for a very long time, and the use of cellulose in the form ofcotton has already been described in U.S. Pat. No. 1,222,883, filed in1915, the combustion of this cotton, distributed in candles containinggum benzoin and styrax as a base being promoted by the absorption ofpotassium nitrate, which makes it possible to obtain a hot flame,required for the combustion of this candle.

The introduction of organic pesticidal compounds, many of which arecapable of being completely and instantly decomposed when heated to atemperature above 700° C., has very rapidly demonstrated thedisadvantages of hot-flame combustion, and has led to work in twodirections. The first direction consists in searching for slow andincomplete combustion which corresponds to a consumption taking place ata lower temperature but frequently producing dirty, and even irritantsmoke. The second direction, which is used more widely nonadays,consists of merely heating the substrate of the active compound untilthe evaporation temperature of this compound is reached.

Belgian Pat. No. 644,414, which dates from 1964, mentions a consumablebody for combating insects, whose combustible substrate is an organic orinorganic substance such as kaolin, silica, pumice, limestone,cardboard, paper, wood, wool or cellulose, impregnated with an inorganicoxidizing agent such as potassium, barium or lead nitrate or withchlorates, and which comprises combustion moderators such as thiourea.

French Pat. No. 2,500,265, filed in 1981 by Roussel Uclaf, alsodescribes, by way of addition, a smoke-forming composition whoseconsumable substrate consists of a mixture of powdered tabu, cedarlevels and pinewood comprising Brilliant Green and para-nitrophenol,such a smoke-forming composition being consumed very slowly, which makesit possible to produce cords known commercially as smoke-forming spiralsor coils, whose rate of combustion may be of the order of a millimeterper minute.

Other compositions of a pyrotechnic kind are also used to distributeeither pesticides or opacifiers (smokescreen) or physiological agents(lachrymatory gases) much more quickly but, because of the higher rateof combustion, these compositions have a higher burning temperature andrelease more smoke. An example of such compositions is mentioned inFrench Pat. No. 2,456,934, which is filed by SNPE in 1979 and relates toa tear-gas grenade whose combustible substrate consists of a polymer, aninorganic oxidizing agent and additives permitting a uniform combustion.

Except for the smoke-forming spirals which are consumed very slowly, itis known that pyrotechnic combustible substrates which comprise aninorganic oxidizing agent and a combustion moderator produce too muchsmoke and burn at a temperature which is a little too high and, forexample, French Pat. Nos. 2,378,448 and 2,382,192 give a gooddescription of these disadvantages.

French Pat. No. 2,378,448, filed in 1978, describes one of the processesfor combating harmful insects which consists in heating a mouldedcomponent made of a porous mineral substance impregnated with an activecompound, by using a rising current of hot air, capable of heating thiscomponent to approximately 200°-430° C. to thus vaporize the activecompound over a short period. This patent refers to a prior art forcombating harmful insects, which consists of burning the combustiblesubstrate (incineration method) in which the active compound isincorporated, and it is indicated that to improve this technique it isnecessary to use a large quantity of active compound but that, despitethis, since the active compound is distributed in a state in which itadheres to the particles of combustion products which are large in size,a sufficient contact between the active ingredient and the insects isnot obtained and the effect produced is weak, it being moreover possiblefor these combustion products in the form of smoke to trigger spuriouslysmoke detectors installed in the buildings.

French Pat. No. 2,382,192, filed in 1978, describes another method ofcombating harmful insects, which also consists of indirectly heating amixture of an active compound and a propagation agent by means of aheating element, to decompose the propagation agent thermally withoutcausing its combustion and to volatilize the active compound. Thispatent contains many comparative tests based on the effect fugacityratio of the active compounds, which is a measure of the efficiency ofthe distribution process and, while, according to this indirect heatingprocess the fugacity ratios lie between 61.1% and 86.7%, comparativetests carried out when using a pyrotechnic composition comprising 30% ofnitrocellulose make it possible to obtain only fugacity ratios ofbetween 1.7% and 8.6%, demonstrating the ineffectiveness of thesepyrotechnic compositions for distributing insecticides, especially ofthe pyrethroid group. This patent, moreover, contains a reminder thatfumigation with compositions of an active chemical material and of acombustible substance which produces heat and smoke while burning is aknown method, and it is stated that, in order to volatilize quickly alarge quantity of the active ingredient, the combustible substance mustbe capable of producing a large amount of smoke. In general, however,this smoke has an irritating odour and is (highly) toxic, and it mayalso suggest the existence of a fire and, furthermore, the soot andother substances which it contains soil the walls, while the combustiblesubstance itself presents a fire risk. This patent then states that themajor disadvantage of known fumigation devices is that the heat ofcombustion of the combustible substance decomposes a proportion of theactive ingrecient, which is thus lost, measurements carried out usingvarious insecticides having given volatilization ratios of less than10%, as stated above.

The purpose of the present invention is to ensure an efficient and rapiddissemination by means of a large volume of combustion gas containingonly very little smoke and originating from a special combustionreaction at a limited temperature so as not to decompose the activecompound, and the invention is characterized in that, on the one hand,the paper is a nitrocellulose-based paper in which the proportion ofnitrogen is greater than 5% and in that, on the other hand, the activecompound has a decomposition temperature above 130° C.

More particularly, the nitrocellulose-based paper consists of a mixtureof binding fibres and of nitrocellulose fibres, this mixture comprisingat least 18% of connecting fibres, at least half of which are cellulosefibres. This nitrocellulose-based paper has a density of between 0.35g/cm³ and 1.3 g/cm³, densities of less than 0.70 g/cm³ being moreeffective both from the standpoint of the ability to fix the activecompound and from the standpoint of combustibility at a moderatetemperature, especially when this nitrocellulose-based paper is between0.2 millimeter and 2.5 millimeters in thickness.

The nitrocellulose-based paper advantageously comprises a proportion ofnitrocellulose-based fibres of between 50% and 75%, this limitingproportion of 50% being desirable to support the exothermicdecomposition reaction of nitrocellulose under the majority ofconditions of use, and this limiting proportion of 75% being required inthe majority of cases to avoid a hot combustion which would take placeat a much higher temperature and which would be unfavourable, it beingpossible for the proportions of nitrogen in the various nitrocellulosewhich are currently usable to vary from 11% to 14%.

The nitrocellulose-based papers may also comprise a resin, but when theactive compound which is to be released is a pesticide, then it ishighly desirable that the resin content of the nitrocellulose-basedpaper be less than 2% because the resins used in the paper industry,which are frequently polymers, increase the volume of smoke which isgiven off and impart an unpleasant irritating odour to this smoke. Onthe other hand, when the active compound to be released is aphysiological agent such as a lachrymatory agent used by the forces formaintaining order, then there is no disadvantage in using resin contentswhich may range up to 6 or 8%, this much higher resin content resultingin the production of more unpleasant smoke, but still making it possibleto maintain an exothermic decomposition reaction of nitrocellulose at alimited temperature.

When the nitrocellulose-based distributing paper is not used promptlyafter its manufacture, which is generally the case, it is then essentialthat this paper contains a stabilizer for nitrocellulose, a stabilizercontent of 0.5 to 1.5% being adequate.

Although the invention enables satisfactory results to be obtained inall cases, and especially when the active compound is incorporated inthe paper, it is preferable that this active compound be not onlydistributed over the paper surfaces but that, on the contrary, bedistributed within the bulk of the paper itself. This arrangementpermits a more homogeneous decomposition reaction of thenitrocellulose-based paper and improves the distribution of the activecompound whose microcrystals or microdeposits on the paper fibres areentrained directly by the hot gases originating from the exothermicdecomposition of nitrocellulose. In fact, during the work concerned withthis invention it was found that nitrocellulose, which is employed inpyrotechnics because its deflagrating properties (gunpowder) and itsproperties of hot combustion which generates gas (propellants), wascapable of decomposing thermally at a relatively low temperature ofbetween 130° C. and 350° C. in intimate combination with cellulosefibres, provided, however, that the reaction was initiated by a suitableignition and took place at atmospheric pressure.

More particularly, the active compound is distributed within the bulk ofthe nitrocellulose-based paper by impregnation in a liquid phase, thebest results being produced with a liquid phase prepared from a liquidbase which is not a solvent which causes nitrocellulose to gel. Theindividual choice of this liquid base depends on the nature of theactive compound and it is preferable that this compound be soluble inthe liquid base used for impregnation, the principal bases which have tobe avoided because of their solvent activity which causes nitrocelluloseto gel being: ether, acetone, tetrahydrofuran, dimethylformamide andcyclohexanone. The liquid base used for impregnation may be chosenespecially from the group consisting of alcohols, methylene chloride,dimethyl sulphoxide, hexamethylphosphotriamide, benzene, toluene andxylene.

The nitrocellulose-based paper impregnated with active compound may beburnt in the open air, but both for reasons of convenience of safety inuse and in transport, and for reasons of effectiveness in distribution,it is preferable that this paper be placed in a pyrotechnic distributorwhich is like a small can provided with openings and fitted with anigniting device. Under such conditions of use, the work concerned withthis invention has shown that the maximum temperature reached in thecentre of the distributor cannot be reduced below 200° C. and, underthese conditions of use, it is then necessary for the decompositiontemperature of this compound to lie above 170° C. to obtain gooddistribution of the active compound in the combustion gases.

The invention is more particularly adapted for the distribution ofactive compounds which contain one or more pesticides and especiallyinsecticides or insect repellents, and the invention has made itpossible to obtain remarkable results to ensure the distribution ofinsecticides belonging to the pyrethroid group, or similar, withpersistent activity, and especially: deltamethrin, tralomethrin,cypermethrin, permethrin, cyfluthrin, cyhalothrin, fenfluthrin,fencythrin and fenvalerate. The efficiency of distribution of suchinsecticides, however, is a function of the temperatures whichcorrespond to the onsets of the thermal decomposition exotherms, and thedistribution of insecticides such as fenvalerate or tralomethrin, inwhich the onsets of the thermal decomposition exotherms occur at 170° C.and at 200° C. respectively does not make it possible to attain themaximum efficiency of distribution when a pyrotechnic distributor isemployed.

The special combustion reaction of the nitrocellulose-based distributingpaper is a self-supporting exothermic decomposition of nitrocellulosewhich takes place without a flame and which is accompanied by a largerelease of gas, the only visible part of which corresponds approximatelyto a large puff of cigar smoke. The formation of such a small quantityof smoke is possible only on the condition that the combustiontemperature does not rise excessively, and to meet this condition itappears to be necessary for the ratio of the active compound to theweight of nitrocellulose-based paper to be less than 0.5, and this isamply sufficient to ensure the distribution of all the testedpesticides, the optimum ratio of the weight of the persistent-effectpyrethroids to the weight of the nitrocellulose-based paper being, forexample, between 0.05 and 0.25.

The nitrocellulose-based distributing paper is preferably in the form ofa strip, which initially makes it easier to impregnate it with theactive compound in a liquid phase, it being possible for thisimpregnation to be carried out continuously on an industrial scaleeither by dipping or by a pressure roller to ensure distribution withinthe bulk of the paper, or by coating according to the techniques used inthe paper industry for surface treatments, a simple sprinkling over oneof the faces of the paper strip, coated with an adhesive beforehand,being possible but producing less effective distribution because of theabsence of dispersion of the active compound between the fibres of thenitrocellulose-based paper. When the nitrocellulose-based distributingpaper is used in a pyrotechnic distributor, it is advantageous for theratio of the length to the width of the strip to lie between 3 and 10,this strip incorporating undulations or folds so as to reduce theregions of contact with the bottom of the distributor, and this makes itpossible, on the one hand, to reduce heating of the walls of thedistributor and, on the other hand, to approach the conditions ofexothermic decomposition in open air, by avoiding any confinement due tothe walls of the can.

Nitrocellulose-based distributing paper strips folded "accordeon-style"are especially suitable for pyrotechnic distributors comprising a canequipped with an igniting device and vents which permit the combustiongases containing the active compounds to leave. More particularly, theratio of the total surface area of the vents to the internal volume ofthe can, expressed in self-consistent units, lies between 0.008 and0.05, which results in a temperature rise in the centre of thedistributor but, to compensate for this, makes it possible for lessinitial heating to be adequate to initiate the decomposition reaction ofnitrocellulose without producing flames. The same operatingcharacteristics lead to a preferential choice of the following ratios(expressed in self-consistent units such as the gram, square centimeterand cubic centimeter):

on the one hand, between the mass of nitrocellulose-based paper and theinternal volume of the can, a ratio which lies between 0.005 and 0.2,

and, on the other hand, a ratio of the total surface area of the ventsto the mass of the nitrocellulose-based paper, a ratio which liesbetween 0.3 and 7.

The pyrotechnic igniting device is advantageously attached in the middleof the top of a cylindrical can and passes through this top, thefrictional initiating composition being external to the can and apyrotechnic delay providing the relay to the pyrotechnic wick which isinside the can and the lighting of which provides the heat inputrequired to initiate the decomposition reaction of the nitrocellulosefibres closely intertwined with the cellulose fibres which are consumed.

The benefits obtained by virtue of this invention consist essentially inthat it is possible to reach an exothermic reaction temperature which issufficiently low to permit the use of the majority of the activecompounds, especially pesticides, which are compounds capable of beingdecomposed by heat more readily than the compounds of the physiologicalagents which may be used, the fugacity ratios obtained for the testedactive compounds being greater than 30% in all cases.

Another benefit which, while not being an essential condition foroperation, is nevertheless highly advantageous, is the considerablereduction in the fumes which are given off despite the rapiddissemination of the active compounds, since it is possible, forexample, to treat a 50 m³ room in 10 seconds while producing only smokeresembling a puff of cigar smoke. The combination of these two benefitsmakes it possible, in fact, to eliminate the two major disadvantages ofthe fumigation processes which have been described in the state of theart in the present description, and, under these conditions, the majortechnical progress contributed by the present invention will make itpossible to use this distribution process not only in buildings, wherevaporization processes relying on electrical heating are currentlyemployed, but also in any partly-closed buildings or enclosures such ascultivation houses which have no electricity supplies and in which theonly treatments which are used at present are thermal fog-spraying of aninsecticide spraying mixture through a venturi or dusting, fumigationtreatments not being used despite their convenience and their speed,because the decomposition which they produce in the active compounds ismuch too excessive as a result of too high a combustion reactiontemperature.

The invention is described in more detail in the following text with theaid of comparative experimental data and examples of implementation, andwith the aid of a drawing in which the single FIGURE shows, in axialsection, a cylindrical pyrotechnic distributor according to theinvention, which makes use of a charge of nitrocellulose-baseddistributing paper.

At present, the only applications of nitrocellulose-based papers are ofa military nature, since virtually all the production capacity permitsthe manufacture of combustible cartridges for high-calibre ammunition,the burning of this nitrocellulose-based paper taking place at a veryhigh pressure in gun barrels. Two manufacturing processes are employed;the first process developed was the process for direct nitration ofpaper, which is immersed in a vat containing the sulphuric-nitricnitration mixture, and the second process, which is more recent, employspapermaking techniques, the thick pulp being spread into a sheet,drained of liquid by rolling and then dried. This second process enablesthe nitrogen content of the paper to be determined with great accuracybecause the paper pulp is prepared by mixing binding fibres, such aspure cellulose fibres, with nitrocellulose fibres whose nitrogen contentis very accurately known and, what is more, this process ensures a morehomogeneous distribution of the nitrocellulose fibres in the bulk of thepaper, particularly when the latter is thicker.

Many nitrocellulose-based paper formulations have been produced and, forexample, the results cited in Table 1 were obtained by preparing thenitrocellulose-based pulp with, on the one hand, shredded kraft paper asa source of cellulose fibres and, on the other hand, nitrocellulose witha nitrogen content of 13.48%, the stabilizer employed beingdiphenylamine, and various proportions of the flocculating resin (anacrylic emulsion) being added.

                  TABLE 1                                                         ______________________________________                                        Nitrocel                                                                              % of      Density  Mass  Time   Temp.                                 paper   nitrocel. (g/cm.sup.3)                                                                           (g)   (s)    (°C.)                          ______________________________________                                        1       68        0.46     5.6    7     173                                   2       65        1.02     5.0   11     155                                   3       65        0.48     5.0    8     131                                   4       57        0.84     5.2   19     148                                   5       50        1.22     5.1   47     138                                   6       50        0.50     5     49     127                                   7       35        0.38     5.3   extinction                                                                           --                                    ______________________________________                                    

In this table:

the left-hand column shows the number of the specimen ofnitrocellulose-based paper,

"% of nitrocel." corresponds to the percentage of nitrocellulose,

"density" corresponds to the density of the specimen,

"mass" corresponds to the total mass ignited

"time" corresponds to the time for complete combustion and

"temp." corresponds to the temperature of flame-free decomposition ofnitrocellulose within the paper.

Specimens 1, 4 and 6 contain 6% of acrylic emulsion.

Specimens 5 and 7 contain only 3% of acrylic emulsion.

Specimens 2 and 3 contain no resin.

Experiments have shown that the temperature of flame-free decompositionof nitrocellulose in the paper was virtually unchanted when the ratio ofthe weight of the active compound to the weight of thenitrocellulose-based paper was less than 0.2. Above this value thecombustion time increases slightly and the temperature recorded tends todrop. Smoke emission is always very low but above a flocculation resincontent of 2% the smoke is irritant, and the irritant effect isproportionately more pronounced the greater the mass of the specimen.This irritant effect is completely useless when pesticides such asinsecticides, insect-repellents, acaricides or fungicides and the likeare distributed, with the exception, however, of the distribution ofchloropicrin, for example, because in this case the aim is to dislodgemammals, and especially foxes, from their lairs. In the course of testscarried out using higher resin contents it was found that thenitrocellulose-based paper itself has no insecticidal effect. On theother hand, the irritant effect of the combustion gases presents nodisadvantage during the release of physiological agents such as teargases; on the contrary, it enhances the efficiency of action of thesephysiological agents.

A lachrymatory nitrocellulose-based paper was prepared from thefollowing paper formulation:

75% of nitrocellulose containing 12.7% of nitrogen

18% of inert long fibres (mixture of cellulose vegetable fibres and ofsynthetic polyester fibres)

6% of acrylic resin

1% of diphenylamine,

this paper, prepared so as to have a density of 0.8 g/cm³, being soakedto saturation with a liquid impregnation phase consisting of 7% ofortho-chlorobenzaldehydemalononitrile (CS) dissolved in benzene. Afterdrying, 5 grams of lachrymatory nitrocellulose-based paper are ignitedby contact with an electrically-heated resistance wire. The effect ofphysical discomfort is such that it is possible to enter a roomapproximately 20 m³ in volume only with difficulty, even after thewindow has been opened for 1 minute. The fugacity ratio of CS ispractically 100%, since its decomposition temperature is close on 600°C., whatever the percentage of CS relative to benzene, since thispercentage was varied from 0.5% to 13% in the tests which were carriedout.

Tests relating to the distribution of pesticides were carried out usinginsecticides, which provide a wide range of thermal decomposition andare highly efficient, and especially using persistent-action pyrethroidsor similar compounds. The thermal decomposition characteristics of themain insecticides tested are collated in Table 2.

                                      TABLE 2                                     __________________________________________________________________________            Decomposition                                                                         Percentage of compound                                        Principal                                                                             exotherms                                                                             remaining after 15 seconds'                                   active  Begin-  heating at T(°C.)                                      compounds                                                                             ning                                                                              End 150°                                                                      200°                                                                       250°                                                                       270°                                                                       300°                                                                       330°                                __________________________________________________________________________    Tralomethrin                                                                          170°                                                                       200°                                                                       -- --   30%                                                                               8% --  --                                         Fenvalerate                                                                           200°                                                                       260°                                                                       90%                                                                              55% --  55%                                                Deltamethrin                                                                          250°                                                                       320°                                                                       -- --  100%                                                                              85% 45%  7%                                        Cypermethrin                                                                          270°                                                                       330°                                                                       -- --  --  75% 70% 70%                                        Permethrin                                                                            270°                                                                       330°                                                                       -- --  --  100%                                                                              90% 80%                                        __________________________________________________________________________

In this Table 2, the decomposition exotherms are obtained by introducingthe active compounds into a high-pressure sealed cell and the rate oftemperature increase is 5° C. per minute from ambient temperature. Onthe other hand, to study the thermal decomposition, the active compoundsare merely introduced into a glass tube and are heated to the indicatedtemperature by means of a metal bath; after a period of 15 seconds atconstant temperature, they are abruptly cooled. The time for thetemperature to rise, which is not taken into account, is also 15 secondsin order to reach a temperature of 300° C. This period of 15 seconds atconstant temperature is situated in the preferred range of times ofcombustion of the nitrocellulose-based papers shown in Table 1, which issubstantially from 7 seconds to 20 seconds.

Table 2 shows that the widest variation in the percentage of insecticidewhich remains active when the temperature varies between 250° C. and330° C. is shown by deltamethrin, and consequently it is when thisinsecticide from the group of light-stable pyrethroids is used that thebiological tests are the most highly sensitive and the most searching,this sensitivity above 270° C. being responsible for some scatter in thevalues observed in the experiments.

Consequently, the thermal decomposition of deltamethrin was investigatedin detail in order to obtain supplementary data permitting aninterpretation of the tests for efficiency with various insects, and theresults of this investigation are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                      Maximum    Decomposition                                                      temperature                                                                              after                                                Heating time  reached    heating                                              ______________________________________                                        30 s          242° C.                                                                           10%                                                  30 s          295° C.                                                                           20%                                                  14 s          309° C.                                                                           30%                                                   5 s          313° C.                                                                           20%                                                   5 s          358° C.                                                                           77%                                                  ______________________________________                                    

To perform the various tests carried out using deltamethrin, thisinsecticide was dissolved in methylene chloride, which is not a solventwhich gels nitrocellulose, and this liquid impregnation phase wasprepared by dissolving from 0.1 to 0.2 g of deltamethrin per cubiccentimeter of methylene chloride, this dosage of 100 to 200 milligramsof deltamethrin being capable of being absorbed directly within the bulkby a quantity of nitrocellulose-based paper of between 0.75 g and 2 g.Other solvents for deltamethrin which neither dissolve nor gelnitrocellulose could be used, such as benzene, xylene or HMPT. Todetermine with a high degree of accuracy the quantity of deltamethrinimpregnating the rectangular specimens of nitrocellulose-based paper,all the depositions of the liquid impregnating phases were carried outby means of a pipette on the surface of the paper in order that theliquid phase might wet the entire surface. The liquid phase migratesvirtually instantaneously throughout the thickness of the paper,especially when the thickness is less than 2.5 millimeters and when thedensity of the paper is less than 0.7 g/cm³. A study with an electronmicroscope shows that deltamethrin crystallizes preferentially on thecellulose fibres and the photographs show excellent adhesion ofdeltamethrin to all the fibres, with the microcrystals coating thesefibres and especially those of nitrocellulose. The microcrystals aremore numerous in the vicinity of the faces of the nitrocellulose-basedpaper, but the distribution within the mass is quite homogeneous whenthe paper thickness is less than one millimeter, it being possible toimprove the homogenization by slowing down the evaporation of methylenechloride which normally evaporats after 5 to 10 minutes' exposure inopen air.

Other tests on the incorporation of active compounds in thenitrocellulose-based paper were carried out, especially by dusting ontoone of the paper, glue-coated beforehand, and by coating one of thefaces with a doctor blade, it being possible for this last process to beadapted to industrial scale by means of coating methods which are usedfor surface treatments in the paper industry, either using a doctor badeor "size-press" rolls.

Comparative tests of dissemination of active compounds were carried outby means of the pyrotechnic distributor shown in FIG. 1 in axiallengthwise section. The active part of the distributor consists of ametal can (1) which is provided with a central igniting device (2) andwhich contains at least one piece of distributing paper (3), and of aremovable plastic lid (4) ensuring sealing during storage and transport.The metal can has a bottom (5) crimped onto the cylindrical shell (6),and when this subassembly has been filled the diffusion lid (7) is alsocrimped onto the top of the cylindrical shell. This diffusion lidcomprises two diametrically opposed circular vents (7a) and apyrotechnic match (2) which is attached in the middle, the frictionalinitiating composition (8) being external to the can. This pyrotechnicmatch has a pyrotechnic delay (9) of 5 seconds and a relay charge (10)consisting of a wick impregnated with black powder. The distributingpaper charges which were tested were 0.5 g, 1 g, 2 g and 4 g ofnitrocellulose-based paper impregnated with deltamethrin in a proportionof 50 mg, 100 mg and 200 mg per gram of nitrocellulose-based paper. Thepieces of distributing papers (3) are rectangular and are placedrandomly inside the can.

The pyrotechnic distributor is used by removing the plastic lid (4) and,if appropriate, clamping it onto the bottom (5) of the can (1) in thecase where the distributor needs to be put on a surface which isparticularly heat-sensitive. The initiating composition (8) is initiatedby rubbing either on the striking surface of a matchbox or on a strikingsurface attached to the lid (4), and this initiating composition ignitesthe delay (9) which burns slowly until the wick (10) impregnated withblack powder produces a considerable flow of heat towards the pieces ofdistributing paper, the few flames which are produced always remainingin the can and never rising up to the vents (7a). The flow of heatgenerated by the igniting device initiates the exothermic decompositionreaction of nitrocellulose which is accompanied by a high release of gasand these gases, accompanied by a little smoke which may originateessentially from the combustion of the binding fibres, entrain theactive compound through the vents and are rapidly disseminatedthroughout the enclosure in which the pyrotechnic distributor is placed.

The results of tests given hereinafter correspond to the use of apyrotechnic distributor whose metal can is 45 millimeters in diameterand 62 millimeters in height, the diameters of the two vents being 10millimeters.

Despite these very modest dimensions, temperature measurements carriedout with a thermocouple show weak heating of the metal can, the maximumtemperatures reached being substantially a function of thenitrocellulose content of the nitrocellulose-based paper, of the mass ofpaper placed in the distributor box and of the type of ignitor used. Forexample, by experimentally removing the pyrotechnic match and by usingan electrically-heated wire placed temporarily in contact with thedistributing paper until the exothermic decomposition reaction ofnitrocellulose becomes self-supporting, the results reported in Table 4were obtained with the use of a nitrocellulose-based paper impregnatedat 100 mg per gram of inert active compound and containing 65% ofnitrocellulose with a nitrogen content of 13.48% (the nitrogen contentof the nitrocellulose-based paper being 8.79%).

                  TABLE 4                                                         ______________________________________                                                         Maximum internal                                             Mass of nitrocellulose-                                                                        temperature (after                                           based paper      5 to 9 seconds)                                              ______________________________________                                        1 gram.sup.      220° C.                                               2 grams          250° C.                                               3 grams          300° C.                                               4 grams          320° C.                                               ______________________________________                                    

Tests to determine the hot combustion thresholds of thenitrocellulose-based papers have shown that these thresholds were also afunction not only of the nitrocellulose content of thenitrocellulose-based paper and of the nitrogen content of thisnitrocellulose, but were also a function of the mass of paper and of theignition heat flow characteristics. For example, when the only parameterwhich was changed was the content of nitrocellulose with a nitrogencontent of 13.8%, and using the same pyrotechnic match and the same massof 2 grams of nitrocellulose-based paper impregnated with deltamethrinin a proportion of 0.2 g per gram of paper, this mass of paper beingplaced in the distributor specified above, the maximum temperature of300° C. was reached after 5 seconds when a nitrocellulose-based papercontaining 65% of nitrocellulose was used, whereas the maximumtemperature reached 410° C. after 3.2 seconds when anitrocellulose-based paper containing 73% of nitrocellulose was used.

The following results were obtained by taking once again the samecharacteristics as those defined above for the nitrocellulose-basedpaper containing 65% of nitrocellulose and by varying the length of thewick impregnated with black powder which is situated at the end of thepyrotechnic match. With the length of the wick doubled, the temperaturerecorded under the same conditions changes from 300° C. to 340° C.; onthe other hand, with the length of the wick shortened by one half, therecorded temperature changes from 300° C. to 250° C.

The temperatures recorded in contact with the outer surfaces of themetal can reach maximum values at the end of the emission of the gasesdue to the decomposition of the nitrocellulose, this emission timevarying substantially from 3 seconds to 12 seconds. When the samecharacteristics as those defined above are adopted again, namely:

2 grams of nitrocellulose papers, 0.8 mm thick, with the followingcomposition:

65% of nitrocellulose fibres whose nitrogen content is 13.8%

34% of cellulose fibres

1% of stabilizer,

0.4 gram of active compound (pyrethroid or CS) distributed within thebulk of the paper by impregnation,

a metal can with φ=45 mm and height=62 mm, with a pyrotechnic matchwhose end with the impregnated wick is situated level with the outersheath,

the maximum surface temperatures (means of the readings) obtained after6 seconds are as follows:

bottom: 85° C.

shell bottom: 65° C.

shell top: 75° C.

lid: 105° C.

The availability of highly advantageous thermodynamic characteristicsmakes it possible to ensure efficient and rapid distribution of thevarious active compounds which may be employed, and the most searchefficiency measurements have been obtained with an insecticide of thepyrethroid group which is particularly heat-sensitive: deltamethrin,which is, furthermore, one of the most efficient insecticides at thepresent time and whose temperature-sensitivity characteristics are shownin Tables 2 and 3 below.

Not all the deltramethrin impregnating the nitrocellulose-based paper isdistributed from the pyrotechnic distributor, since analysis of theresidual ash in the metal can shows that from 4 to 12% of thisinsecticide is left in this ash. To reduce this percentage it isnecessary to raise the internal temperature in the distributor, and thisappears automatically to entail a high degree of deactivation ofdeltamethrin and tests have shown that, to achieve a maximum actualefficiency, which corresponds to a fugacity ratio of more than 50%,there was no point in reducing the percentage of deltamethrin in the ashbelow 8 to 10%.

The intrinsic efficiency of deltamethrin is a function of the ambienttemperature and of the ambient relative humidity, this insecticide beingslightly more effective when the temperature is close to 20° C. and whenrelatively humidity is low. These two factors partly explain thedifferences observed during entomological trials, the relative sealingof the various buildings or closed enclosures being a third factor whichaffects the experimental results which were obtained:

in the various buildings used:

conventional silos with a volume of less than 50 m³,

warehouses or stores capable of ranging up to 500 m³,

modern horizontal and vertical silos, up to 10 m in diameter and 60 m inheight,

in cultivation enclosures such as:

"Nantes-type" tunnels 0.5 to 0.6 m in diameter and approximately fiftymeters in length,

plastic hothouses 3 m in diameter and 25 m to 100 m in length, and

glasshouses 6 m in width and 3 m in height, with a length of 25 m.

The results obtained in a laboratory closed room (a 50-m³ Peet & Gradyroom), at 23° C. with a constant relative humidity of 60%, have shownthat the use of 0.8 g of nitrocellulose-based paper in the pyrotechnicdistributor is sufficient to obtain total knockdown of the followingbiological indicators after 16 hours: Musca domestica (diptera),Spodoptera littoralis (caterpillars) and Rhizopertha dominica (Coleopterbostrychides). The nitrocellulose-based paper used contained 65% ofnitrocellulose (13.8% of N₂) and the deltamethrin impregnation was onlywith 0.1 g per gram of nitrocellulose-based paper. Despite this lowdosage of insecticide, it was found that the threshold for 50% knockdownof house flies (KT₅₀ for Musca domestica) was reached after 20 min. Thesame nitrocellulose-based paper, but used in a dosage of 1 g in thedistributor, and impregnated with deltamethrin in a proportion of 0.2 gper gram, enabled 100% mortality of cockroaches Periplaneta americana tobe obtained after 35 minutes.

The first tests carried out in actual cultivation structures weredeliberately performed under the worst sealing conditions, whereas thelaboratory tests had been performed in a hermetically closed room. Thesetests were carried out on the Crau plateau on a day with a violentmistral (wind from 80 to 100 km/hour) in hothouses of the plastic tunneltype, of standard manufacture, kept nonhermetically closed only for onehour after the use of the pyrotechnic distributor. The hothouses had alength of 100 m and a cross-section of a wide elliptical segment 7 m inwidth and 2.5 m in height. The biological indicators comprised adults ofMusca domestica (M.d.), caterpillars (L4) of Spodoptera littoralis(S.l.), adults of Acanthoscelides obtectus (A.o. Coleoptera bruchides)and the adults of Aphis craccivora (A.c. Cowpea aphid). Thenitrocellulose-based paper used also contained 65% of nitrocellulose(13.8% of N₂) and the deltamethrin (M) impregnation was with 0.1 or 0.2g per gram of paper. The results obtained are listed in Table 5, eachvalue shown being the mean of two or three tests carried out under eachof the test conditions.

                  TABLE 5                                                         ______________________________________                                        Pyrotechnic distributors                                                      M               No. of   Knockdown rate after 1 hour                          dosage M paper  cans     M.d.  S.l.  A.o.  A.C.                               ______________________________________                                        0,1 g/g                                                                              1 g      5        100%  90%   30%   100%                               0,1 g/g                                                                              1 g      3        80%   80%   50%   100%                               0,2 g/g                                                                              2 g      3        98%   90%   45%   100%                               0,1 g/g                                                                              3 g      2        95%   70%   55%    90%                               0,2 g/g                                                                              3 g      2        90%   85%   60%   100%                               ______________________________________                                    

distributed uniformly along the greenhouse and were ignitedsimultaneously. The periods for which the greenhouses are closed fortreatment are generally from 8 hours to 12 hours, and the knockdown rateafter 1 hour is therefore merely an indication of efficiency which is ofgreat interest but which does not correspond to actual knockdown rates(except for the 100% rate) which may be obtained with normal periods ofclosure and a weak wind, the absence of wind being undesirableespecially when the distributors are at some distance from each other.For example, the complete destruction of caterpillars of Spodopteralittoralis was obtained over periods from 3 h 30 to 5 h in the sameplastic greenhouse on days with a weak wind and without wind, byarranging 3 distributors, each containing 4 grams ofnitrocellulose-based paper impregnated with deltamethrin in a proportionof 0.05 g per gram of paper. The knockdown rate for Aleurodes(Hemiptera) in greenhouses of the plastic tunnel type remains lesssatisfactory at present, but the only tests which were carried outinvolved distributors whose fugacity ratio was only 45%. Other testsperformed in the laboratory closed room have enabled knockdown rates of80% and even 98% to be attained after a contact time from 4 hours to 15hours.

Other tests were carried out to measure the efficiency of distributionof insecticides over insects of stored foodstuffs, and three Coleopteracurculionides were chosen:

Sitophilus granarius (S.g.), which attacks chiefly wheat,

Sitophilus oryzae (S.o.) which attacks chiefly rice, and

Tribolium castaneum (T.c.) which attacks chiefly flour.

The tests took place in the 50 m³ laboratory closed room, which ishermetic, and this corresponds substantially to actual conditions, sincesilos or warehouses are quite well sealed. The three species of weevilswere arranged in various manners:

in direct contact with the atmosphere of the room,

in indirect contact, the insects being capable of withdrawing from thetreated atmosphere by burrowing into a 2 cm layer of wheat, rice orflour, and in a hidden position under a polystyrene box the base ofwhich was pierced with holes enabling the insects to pass.

In the case of the tests carried out with deltamethrin, these testspermitting a more direct comparison with the described preceding tests,a single pyrotechnic distributor was placed on the floor in the room,and the results listed in Table 6, for example, were obtained using onlyone gram of nitrocellulose-based paper impregnated either with 0.2 g ofdeltamethrin (M) or with 0.1 g, the test contact times being 4 hours and16 hours, and monitoring being carried out either 4 hours or 7 daysafter the contact time.

                  TABLE 6                                                         ______________________________________                                        Percentages of mortality                                                                                   0,1 g                                                          0,2 g of ΔM                                                                            of ΔM                                                    4-hour  16-hour                                                               contacts                                                                              contacts                                                              monitoring                                                                            monitoring                                              Conditions Insects  4 h    7 d  4 h  7 d   4 h                                ______________________________________                                        Direct contact                                                                           Sg       100    100  100  100   100                                on the ground                                                                            So        50     60  100  100   100                                           Tc       100    100  100  100   100                                Direct contact                                                                           Sg       100    100  100  100   100                                at 2 m height                                                                            So       100    100  100  100   100                                           Tc        90     95  100  100    96                                Indirect con-                                                                            Sg       100    100   92   92    90                                tact on the                                                                              So        40     45   36   28    80                                ground     Tc        16     16   95   25    48                                Indirect   Sg       100    100  100   70    95                                contact    So       100    100  100   80    90                                           Tc        20     15   85   20    25                                Hidden     Sg       100    100   95  100   --                                 position   So       100    100   95  100   --                                            Tc        98     98   98   80                                      ______________________________________                                    

We claim:
 1. A composition capable of disseminating an effective amountof an insecticide, an insect repellant or a lachrymatory agent whichconsists of (1) a combustible substrate and (2) said insecticide, insectrepellant or lachrymatory agent; said combustible substrate is paperconsisting essentially of a mixture of binding fibers and 50-75%nitrocellulose fibers, said paper having nitrogen content greater than5%, said insecticide, insect repellant or lachrymatory agent having adecomposition temperature above 130° C.
 2. The composition according toclaim 1 wherein said insecticide, insect repellant or lachrymatory agentis distributed within the bulk of said paper.
 3. The compositionaccording to claim 1 wherein said insecticide, insect repellant orlachrymatory agent is distributed within the bulk of the paper byimpregnation in a liquid phase, said liquid phase being made from aliquid base which is not a solvent capable of gelling nitrocellulose,wherein said insecticide, insect repellant or lachrymatory agent issoluble in said liquid impregnation base.
 4. The composition accordingto claim 1 wherein the ratio of the weight of said insecticide, insectrepellant or lachrymatory agent to the weight of said paper is between0.05 and 0.5.
 5. The composition according to claim 1 wherein saidinsecticide, insect repellant or lachrymatory agent has a decompositiontemperature above 170° C. of bonding fibers which are a mixture ofcellulose fibers and synthetic polyester fibers, 6% by weight acrylicresin, 1% by weight diphenylamine and 7% of the lachrymator agentorthochlorobenzaldehydemalononitrile.
 6. The composition according toclaim 1 wherein said paper additionally contains up to 2% of aflocculating resin.
 7. The composition according to claim 1 wherein saidpaper comprises at least 18% of binding fibers and at least one half ofsaid binding fibers are cellulose fibers.
 8. The composition accordingto claim 1 wherein said paper has a density between 0.35 g/cm³ and 1.3g/cm³.
 9. The composition according to claim 8 wherein the thickness ofthe paper is between 0.2 millimeter and 2.5 millimeter.
 10. Thecomposition according to claim 9 wherein the paper comprises 0.5-1.5% ofa stabilizer for nitrocellulose.
 11. The composition according to claim3 wherein said liquid base is a member selected from the groupconsisting of alcohols, methylene chloride, dimethyl sulfoxide,hexamethylphosphotriamide, benzene, toluene and xylene.
 12. Thecomposition according to claim 1 wherein said paper is in the form of astrip.
 13. The composition according to claim 1 wherein said insecticideis a member of the pyrethroid group.
 14. The composition according toclaim 1 wherein said insecticide is deltamethrin, tralomethrin,cypermethrin, permethrin, cyfluthrin, cyhalothrin, fenfluthrin,fencythrin or fenvalerate.
 15. The composition according to claim 13wherein the ratio of the weight of the pyrethroid to the weight of saidpaper is between 0.05 and 0.25.
 16. The composition according to claim 1wherein the nitrogen content of said nitrocellulose is 11-14% by weight.17. A lachrymatory composition comprising 75% by weight nitrocellulosecontaining 12.7% nitrogen, 18% by weight of bonding fibers which are amixture of cellulose fibers and synthetic polyester fibers, 6% by weightacrylic resin, 1% by weight diphenylamine and 7% of the lachrymatoragent orthochlorobenzaldehydemalononitrile.